Recent investigations in our laboratories have focused on the influence of peripheral substituents and axial ligands on the properties of metalloporphyrin complexes. We have found that as the substituents become increasingly electron-withdrawing the resulting metalloporphyrins show less tendency to aggregate, have greater tendency to add axial ligands, undergo substitution reactions more slowly and are more easily reduced. We have found that metalloporphyrin properties are markedly influenced by the nature of the axial ligand(s) as well; a very large trans effect has been found for complexes of tetra (4-N-methylpyridyl)porphine cobalt(III) and tetracarboxyphenylporphinatocobaltate(III). We plan to use our knowledge attained from these studies to prepare and study iron porphyrin complexes and metalloporphyrin-protein complexes. A variety of spectral, kinetic and magnetic techniques will be used to investigate the aggregation, ligation, and redox properties of these substances. From this work we hope to achieve a clearer understanding to the mechanisms of biochemical action of the model systems and the native substances.